Cathode ray beam deflection circuits



July 5, 1955 L. M. LEEDS 2,712,615

CATHODE RAY BEAM DEFLECTION CIRCUITS Filed Jan. 25, 1952 hverwtm Lauren/wee M. Leeds,

@3Q/m ABM His Attovhey.

CURRENT l C t fr rgert cala'oor. aar BEAM onrLnc'rroN crncurrs Lanrance ivi. Leeds, Syracuse, N. Y., assigner to General ectric Company, a corporation of New York Application January 25, 15,352, Serial No. 268,195

2 Claims. (Cl. 315-27) The present invention relates to cathode ray beam deliection circuits and has for a general object to provide improvements in circuits of this kind making use of electron discharge devices in shunt with the deection coils as self-oscillation Suppressors in the deiection coil circuits.

lt has been found that in cathode ray deflection circuits of the latter kind making use of a transformer to supply currents from a source to the deilection coils, small variations in the characteristics of the transformers or the electron discharge devices as well as other changes in the deflection circuits will cause the current through the deilection coils to vary non-linearly with time.

The present invention is directed to circuits for making it possible to use transformers and oscillation suppressor electron discharge devices of greater tolerance without appreciable sacrifice in linearity. To this end a deflection circuit, and particularly the characteristics of the transformer and the oscillation suppressor electron discharge devices connected in shunt with the deiiection coil, is arranged so that the initial decay of current in the deflection coils from one extreme value at the initiation of the detlection from this extreme is slower than for a linear deection, i. e., the oscillation suppressor circuits overdamp the current oscillations in the deection coils. A resistance is located in series with the electron discharge path of the oscillation suppression device to decrease the damping eifect of the oscillation suppression device to compensate for departures in linearity of current flow through the deflection coils.

The novel features which i believe to be characteristic l.

of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. l is a schematic representation of deflection circuits embodying my invention; Fig. 2 is a group of diagrams used to explain the operation of the embodiment of my invention shown in Fig. l.

Referring now to Fig. l, there is shown an electron discharge device 1 providing cyclically varying currents comprising a cathode 2 connected through a cathode resistance 3 shunted by a by-pass capacitor 4 to ground and to the negative terminal of source of unidirectional potential 5, an anode 6 connected through parasitic suppressor resistance 7, the primary winding 8 of transformer 9 and decoupling resistance 1t) by-passed to ground by decoupling capacitor 10 in that order to the positive terminal 1l of the source 5, a control grid 12 connected through grid leak resistance 13 to ground and to terminal 13 and through coupling capacitor 14 to terminal 15 between which and terminal 13 is applied a voltage varying with time of a kind shown in and to be described further in connection with Fig. 2. The screen grid 16 is connected through voltage dropping resistance 17 to the positive 2,7l2,6l5 Patented July 5, 1955 terminal 11 and through lter capacitor 18 to ground. The suppressor grid i9 is connected to the cathode 2.

One terminal 20 of cathode ray beam deiiection coil 21 is connected to an intermediate point 22 on the secondary winding 23 of transformer 9. The other terminal 24 of the detlection coil 2l is connected through a centering resistance 25 to an end terminal 26 of the secondary winding 23, and is also connected through resistance 27 to ground. Terminal 25 of secondary winding 23 is connected through resistance 2S to ground. Resistance 25 has a variable tap which is connected to the negative terminal of a source of unidirectional potential 29, the other terminal of which is connected to ground, in order to provide a variable unidirectional current through the dellection coil for cathode ray beam centering purposes.

A pair of electron discharge devices 3l) and 3l each including, respectively, cathodes 32 and 32 connected together and to terminal 26 of secondary winding 23, anodes 33 and 34 connected together and through unbypassed damping resistance to the other end terminal 36 of the secondary winding 23, and grids 37 and 38 is provided. A rentiating and biasing network comprising differentiating capacitor 39, bias resistor 4% shunted by bypass capacitor 41, and ditferentiating resistance 42 connected in that order in series between the junction of the anode 33 the damping resistor "i5 and ground is also provided. The grids 37 and S are connected through isolating resistances i3 and 442, respectively, to the junction of capacitor 39 and resistance dil.

Referring now to Fig. 2, there are shown graphs of voltage and current useful in explaining the operation of the circuit of Fig. 1. in graph 45, the abscissa represents time and the ordinate represents the general form of the voltage wave applied between terminals 15 and 13 of Fig. l. ln graph 46, the abscissa represents time and the ordinate represents current flowing through deflection coil 2l with no damping resistor 35 in the circuit of Fig. 1. ln graph 47 the abscissa represents time and the ordinate represents current flowing through deflection coil 21 with damping resistor 35 in the circuit. The graphs of Fig. 2 are drawn to the same time scale and points on the graphs lying in a straight line perpendicular to the time axis represent generally simultaneous conditions of voltage and current in the circuit of Fig. l.

Referring now to the operation of the circuit of Fig. l, a voltage represented by graph 5 of Fig. 2 is applied between terminals 15 and 13. As the voltage at grid 12 increases from point SS of graph 45, the current through the device i and hence through the transformer 9 and the detiection coil 2l increases as shown in curve de, causing the cathode ray beam of a cathode ray tube (not shown) operative from deection coil 21 to move from a center position to one side. At a time represented by point 49, the voltage on grid l2 is driven negative very rapidly, causing electron -discharge device 1 to become nonconductive and causing a momentary self-oscillation in deflection coil 21-transformer 23 circuit at a frequency determined approximately by the self inductance of the deection coil 2i and all of the distributed capacitances of the deflection coil, transformer, and circuit as reflected across the deflection coil. This frequency of self-oscillation is such that the first half-cycle occurs approximately lduring the time interval represented between points 49 and 59 on graph 45. During the iirst half cycle of this self-oscillation, the voltage at terminal 20 of deection coil 21 changes to a maximum negative value and returns to zero while the current in the deflection coil changes from its maximum positive value passing through zero to a maximum negative value. As the oscillation tends to continue beyond this half cycle, the voltage at terminal 2t) attempts to continue through zero and become positive with respect to terminal 26 of secondary winding 23, causing damping electron discharge devices 30 and 31 to conduct and to damp deflection oscillation in the transformer-coil circuit to cause a gradual decrease of current in the dellection coil 2?. instead of undesirable oscillatory variations of current at high frequency which disturb the linear variation of current in coil 21.

In order to sufficiently damp the above-mentioned current oscillations, it is generally necessary to connect the damping devices 39 and 31 in shunt with the entire secondary winding 23 including extended winding 23'. By this means, an auto transformer action is obtained such that a greater positive change of voltage is obtained at terminal 35, and hence across the damping devices 30 and 31, than is present at terminal 22, to which terminal 20 of deflection coil 21 is connected.

Additionally, in order to obtain sutlicient damping particularly at the start of the deflection, the differentiating circuit including capacitor 39 and resistance 42 differentiates the initial change in voltage appearing across the deflection coils and extended winding, if used, and applies this voltage between the grid and cathode of the damping devices 30 and 31 in a manner to cause these devices to conduct very heavily to substantially damp the abovedescribed oscillations. Two devices have been used in parallel to permit very large damping currents to flow.

From the instant 50, the current through the deflection coil 21 -decreases in magnitude along curve 46 for substantially one-half the duration of the gradually increasing portion of the sweep voltage 45. Near the point 51 where zero current llows through the deflection coil, the electron discharge device 1 is again caused to conduct. The voltage 45 causes the current 46 to increase again up to the time represented by point 52.

It has been found that in order to obtain linear change of current during the initial portions of the rising current portions of graph 46, the transformer secondary winding 23 and the damping devices 3i) and 31 must be very carefully selected in order to provide just the right amount of damping to obtain the linear sweep. It has also been found that the leakage reactance between the transformer windings represented by terminals 26-22 and 22-36 must be rigidly controlled, as well as the number of turns, tension on the wire when winding the coils, magnetic properties of the core material and the form, spacing, and lay of the wires constituting the coils. ln fact, in or-der to obtain exceedingly linear deflection, the manufacturing tolerances of the transformer must be so precise as to make the transformer exceedingly costly and dilcult to manufacture.

It has further been found that the damping circuit in association with electron discharge devices can be overdamped by using an excessive number of turns on the extended winding between terminals 22 and 36 to produce a current wave through the deflection coils of the kind shown in graph 46. With the circuit over-damped, it has been found that exceedingly' precise control of the reduction in damping can be effectuated by means of damping resistance 35. With these provisions, the graph 46 can be made substantially linear as shown in Fig. 2. By overdamping and employing resistance 35 to obtain precise control of the amount of damping, it is not necessary to hold the transformer to very precise manufacturing tolerances, thus obtaining a much less costly design and one which is practical to build.

A damping resistor 35 having a magnitude of about 50 ohms when used with a particular transformer and 6AS7G damping tube corrected a one percent linearity error at the start of the sweep to substantially no measurable error. These values are given as an example, and are not to be construed as limiting the scope of my invention.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications, both in the circuit arrangement and in the instrumentalities employed may be made, and I, therefore, contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What l claim as new and desire to secure by Letters Patent of the United States is:

l. A derlecting circuit for a cathode ray comprising a source of cyclically varying current, a transformer including a primary and a secondary winding, said primary winding connected in energizable relationship to said source` a cathode ray deflection coil connected in shunt with said secondary winding, an electron discharge device including a cathode, a grid, and an anode and having the anode-cathode discharge path thereof connected in shunt with said secondary winding, means for differentiating the voltage appearing across said deflection coil and applying said differentiated voltage between the grid and cathode of said device to control the anodecathode impedance of said device, said secondary winding being proportioned to develop sufficient voltage to cause currents to be developed in said deflection coil which decrease slowly at a gradually increasing rate from one extreme value, then increasing in the opposite direction to another extreme value, and then rapidly decreasing from said other extreme to said one extreme in substantial accordance with the cyclical variation of said source, an unbypassed resistor connected in series with the electron discharge path of said device and having sufcient value to alter the damping of the circuit including said transformer and said discharge path, Whereby said slowly decreasing current is caused to vary linearly from said one extreme to zero.

2. A detlecting circuit for a cathode ray comprising a source of cyclically varying current, a transformer including a primary winding and a secondary winding, said primary winding being connected to said source, a cathode ray deflection coil connected in shunt between one end of said secondary winding and an intermediate point thereof. an electron discharge device including a cathode, a grid, and an anode, said cathode being connected to said one end and said anode being connected to the other end of said secondary winding, means for differentiating the voltage appearing across said secondary y, Winding and applying said differentiated voltage between the grid and cathode of said device, the circuit including said secondary winding and electron discharge device being proportioned to cause currents to be developed in said deflection coil which decrease slowly at a gradually increasing rate from one extreme value to zero, an unbypasscd resistor connected between said anode and said other end of said secondary winding and having such a magnitude as to cause a decrease in current to flow through said device whereby said slowly decreasing current is caused to vary linearly from said one extreme to zero.

References Cited in the le of this patent UNITED STATES PATENTS 2,456,784 Schade Apr. 12, 1949 2,584,268 Hodder et al. Feb. 5, 1952 2,621,237 Huntley Dec. 9, 1952 

